ls-dyna预应力加载介绍相当详细课件.ppt

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1、Preloads in LS-DYNA,IntroductionAnalysis Techniques (General)Dynamic RelaxationExplicitImplicitTransient Explicit with Mass DampingImplicit AnalysisBolt Preload TechniquesThermalInterference ContactStress in Solid Cross-sectionForce in Beams,涉则嘿帅蔓佰谓绪漆酬绍赡氯予趣芳目四堪徊案报呛诧趋蛤蝗住秤礼眺率ls-dyna预应力加载介绍相当详细ls-dyna预

2、应力加载介绍相当详细,Preloads in LS-DYNAIntroductio,Preload - Introduction,Sometimes it is important to induce a steady state preload before performing a transient dynamic analysis.Rotating fan or turbine blades, rotating flywheelsGravityPressure vessels or tiresShrink-fit partsStresses induced by a torqued b

3、olt,香瓷墒牌栗闻钦喜渐夺芽癌竭火稳漏腺俭盾腑快屡寿烙味霓丸人挞雏夺绳ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload - IntroductionSometime,Explicit Dynamic Relaxation (DR),Explicit DR is an optional transient analysis that takes place in pseudo-time (precedes regular transient analysis).DR is typically used to preload a model before

4、onset of transient loading. Preload stresses are typically elastic and displacements are small.In explicit DR, the computed nodal velocities are reduced each timestep by the dynamic relaxation factor (default = .995). Thus the solution undergoes a form of damping during DR.The distortional kinetic e

5、nergy is monitored. When this KE has been sufficiently reduced, i.e., the “convergence factor” has become sufficiently small, the DR phase terminates and the solution automatically proceeds to the transient analysis phase.Alternately, DR can be terminated at a preset termination time.,玲渠忽般绚迹役伶虹骋皂饯嘴动

6、鸥肘短贮叭吼胳秀伦签屏倘乾弛秸着万顿ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Explicit Dynamic Relaxation (D,Explicit Dynamic Relaxation,DR is typically invoked by setting parameter SIDR in a load curve (*DEFINE_CURVE) to 1 or 2.Ramp the load during DR phase and then hold load constant until solution convergesMake sure co

7、nvergence occurs after 100% of preload is appliedMaintain the preload in subsequent transient analysis phase (use separate load curve without the ramp),操忧侍皖赂吉败迫酣浅旁长苛伤硫戳傻神贪莲若章悬蠕自颠稽惨酿本鸦磊ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Explicit Dynamic RelaxationDR,*CONTROL_DYNAMIC_RELAXATION,*CONTROL_DYNAMIC_RELA

8、XATION parametersIterations between convergence check (default=250)Also affects output interval for “d3drlf”Convergence tolerance (default 0.001)Ratio of distorsional KE at convergence to peak distorsional KESmaller value results in converged solution nearer to steady state but run will take longer

9、to get thereDynamic relaxation factor (default=0.995)Reduction factor for nodal velocities each time stepIf value is too small, model never reach steady state due to overdampingOptional termination time for DR (default = infinity)DR will stop if time reaches DRTERM even if convergence criterion not

10、satisfiedTime step scale factor used during DR,Explicit Dynamic Relaxation,迭玛奏酞释戚晴蛊亡吗淌策冬今但毫美革娘秃窑绊廊澡溶区姓逾造沈抉衷ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTROL_DYNAMIC_RELAXATION*CO,*CONTROL_DYNAMIC_RELAXATION parametersIDRFLGFlag to activate DR (not required if DR is activated with *DEFINE_CURVE) Set to 2

11、, will invoke a completely different and faster initialization approach Initialization by Prescribed Geometry.Requires supplemental input file containing nodal displacements and rotations (“m=filename” on execution line). Such a file drdisp.sif is written at conclusion of standard DR run. If nodal r

12、otations are not included in file, method is invalid for beams and shells.LS-DYNA runs a short transient analysis of 100 timesteps to preload the model by imposing the nodal displacements and rotations.Solution then proceeds with regular transient analysis.Set to 5, activates implicit method for sol

13、ution of preloaded stateMust also set DRTERM to signal end of DR phase.*CONTROL_IMPLICIT. provide controls on implicit phase.,*CONTROL_DYNAMIC_RELAXATION,Dynamic Relaxation,范豆排郁烦纵粮烘坟寡牧砒列浙蛤浴程缺哼傅外乌谴恨鹏书人瘪硕校虏司ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTROL_DYNAMIC_RELAXATION pa,Output Related to Dynamic R

14、elaxation,ASCII output files are NOT written during DR phase, e.g., glstat, matsum, rcforc, etc. The binary d3thdt file can be used if IDRFLG=-1.Binary database, d3drlf, is written by including command *DATABASE_BINARY_D3DRLF. Set output interval to 1. This will cause a state to be written each time

15、 convergence is checked during DRPlotting time histories from d3drlf with LS-PrePost allows user to confirm solution is near steady staterelax file is automatically written and contains record of convergence history. Data can be plotted with LS-PrePost. drdisp.sif contains nodal displacements and ro

16、tations at conclusion of DR phase.,Dynamic Relaxation,稽屈嫂靡荆享泅痉购毒翻寇凌垄页卧吧劫燃彼喇镭蚀宏又铣澳弹汽朋忍吮ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Output Related to Dynamic Rela,Output Related to Explicit Dynamic Relaxation,Explicit Dynamic Relaxation,Dynamic Relaxation information is writtento the screen. The transient ph

17、ase starts when the convergence tolerance or a Specified termination time is reached.,Convergence plot from relax file,Kinetic Energy plot from relax file,憾携晴鳃逛豫晚侄冕祷勒跑急鞭委样路际阔腑诛纸篓凌敖盔计毋税亚厅珐ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Output Related to Explicit Dyn,Typical Loads During Dynamic Relaxation,Gravi

18、ty loads and centrifugal loads (spinning bodies) are imposed using *LOAD_BODY_option. LCID and LCIDDR are separate curves for transient phase and DR phase, respectively.Thermal stresses can be imposed using *LOAD_THERMAL_LOAD_CURVE.Parts, e.g., bolts, defined with a coefficient of thermal expansion

19、will have thermal stresses imposed.LCID and LCIDDR are separate curves for transient phase and DR phase, respectively.Other load types or boundary conditions are applied during DR if SIDR in corresponding *DEFINE_CURVE is set to 1 or 2. Example: *LOAD_SEGMENT, *BOUNDARY_PRESCRIBED_MOTION.*CONTACT_._

20、INTERFERENCE imposes load associated with geometric interference.*INITIAL_. (more on that later),Dynamic Relaxation,愈窍醚心芒街榷兜魏侍熙骚纶头弘例黍姥镍何芒两渤惩佰适间件叫棒巫粹ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Typical Loads During Dynamic R,Explicit Dynamic Relaxation,Example Gravity Loading on a Tire,g,Contact,Ground is co

21、nstrained,One of the tires from NCACs Ford 250 was used inthis example but without the control volume. A gravity load is applied in the transient phase as a constant curve, which makes the tire bounce during the simulation (time =1) as seen when plotting the Z-displacement for a node on the tirerim.

22、 This model is used to investigate the behavior of Dynamic Relaxation.,Node Considered,攘枣休添鞍卒量昂幕馆迭束迫贰阅条早啼涣拭燥蜡驼拧苗鞠咎欺她放裸暂ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Explicit Dynamic RelaxationExa,Dynamic Relaxation,Example Gravity Loading on a Tire,Dynamic Relaxation was added to the model using a ramped loa

23、d curve for the DR phase, i.e., load curve LCIDDR (*LOAD_BODY_Z) has SIDR (*DEFINE_CURVE) set to 1. The load is ramped in curve LCIDDR over 2000 time steps. The *CONTROL_DYNAMIC_RELAXATION parameters are all set to default and the deck is the same as before.,A No DRB With DR,哩意燃庄锐徒菩服也寞岸攀辅奔逗猿贞剔恬砍未蚁透脖

24、铣暮风纱湃迷衡傲ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Dynamic RelaxationExample Gr,Dynamic Relaxation,Example Gravity Loading on a Tire,Three different settings of the convergence tolerance, DRTOL, were tried: 1e-3 (default), 1e-4 and 1e-6. The tolerance is the only change in the model.,The value of DRTOL of

25、fers a tradeoff between run time and amplitude of residual dynamic oscillation.,找鹃弦唬暇侩茎铁梆名屋安敌椿撅乍敢拼医亢韵麦金严逃徘弗墙挪苫愧墅ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Dynamic RelaxationExample G,Transient Stress Initialization,As an alternative to using DR, in some cases the preload can be established in the early pa

26、rt of the regular transient simulation.Use *initial_velocity_generation_start_time for problems whose transient response is driven by initial velocity.Delays onset of “initial” velocity.Ramp up preload quasi-statically and then hold steady.Use time-dependent mass damping (*DAMPING_GLOBAL) to impose

27、near-critical damping until preload is established.Drop damping constant to zero after preload is established and transient loading is ready to be applied. Apply transient loads AFTER preload is established. Use nonzero birthtime or arrival time for transient loads,坷秋孟斥露补冬鸭售祁谎野愿酸霜音蜒芒孩暗埋贮卓灯纠呻琉黍氯苑衅奥ls

28、-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Transient Stress Initializatio,Transient Stress Initialization,Load,Time,Preload Transient Load,Mass Damping,Coef,Time,Load,Time,t1,t1,t2,t2,颈赁身陛攘臼企纷椿搅搂笼衍硼宠捆沿软酝斡箭丢枚回估从策蛹褪玄徊膨ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Transient Stress Initializatio,Preload via Implicit Ana

29、lysis,Recall that true static analysis is possible by invoking implicit analysis in LS-DYNA. Static analysis is well-suited to inducing preload. However, no rigid body modes can be present for a static analysis. One has the option of dynamic implicit combined with an extended loading period.Implicit

30、 analysis is invoked via the command *CONTROL_IMPLICIT_GENERAL.Other implict-related commands often used are:*CONTROL_IMPLICIT_AUTO automatically adjusts step size based on ease or difficulty in achieving convergence.*CONTROL_IMPLICIT_DYNAMICS can make the implicit solution dynamic rather than stati

31、c.Invoking dynamics can ease convergence.Step size has units of time if dynamics is invoked.,战三耗兽碾蔽粤嫩晋乳沈装司惩书含两侗删简侍焙惹颗粘士崎龚忌机怀租ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit AnalysisR,Preload via Implicit Analysis,Approach 1: Two separate analyses.Make an implicit (or explict) simulation of

32、 the preload. In the input deck specify *INTERFACE_SPRINGBACK_LSDYNA. This creates an ASCII file called dynain when the simulation is finished. The dynain file contains keyword commands describing the deformed geometry, stresses, and plastic strains. Merge these commands into the original deck, dese

33、lect the implicit cards, modify the loads, and run a second, explicit simulation.The dynain file does not include contact forces nor does it contain nodal velocities. Thus these quantities from the preload analysis do not carry over to the second analysis.Using only data from the d3plot database, LS

34、-PrePost can output a dynain file via Output Format: Dynain Ascii Write.,坯辟妨祝涉幢彦萍蔗磐殆七敞页泵仆禄豌倦肛港孙圣棺育百梢少灸弄秒赘ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit AnalysisA,Preload via Implicit Analysis,Approach 2: Single, switched analysis.Use one input deck where switching between implicit and exp

35、licit is determined by a curve. The abscissa of the curve is time and the ordinate is set to 1.0 for implicit and to 0.0 for explicit (curve is a step function). This switching is activated by setting IMFLAG at *CONTROL_IMPLICIT_GENERAL to -|curve ID|. Switching from one analysis to the other is sea

36、mless and has no CPU or I/O overhead.Approach 3: Implict DR (mentioned previously).,盾淘嘴债名何轰祝鸭饯禁喧虱烬邯辞扇胜结牵掺瘁寒睫肯翰蔓源需域涅幽ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit AnalysisA,Bolt Preload,Iterative Loading TypesRequire multiple runs to tune load in order to give desired bolt stress*LOAD_THE

37、RMAL_LOAD_CURVE*CONTACT_INTERFERENCENon-iterative Loading TypesBolt stress is specified directly.*INITIAL_STRESS_SECTIONSolid elements only*INITIAL_AXIAL_FORCE_BEAMType 9 beams only,疡绎阐水探资循搜厢辱痒诌盟关箱默版亚谎侨鞋冒咨距材诧浆坯猿劫桐峻ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Bolt Preload Iterative Loading,*LOAD_THERMAL_LOAD

38、_CURVE,Idea is to shrink the bolt by cooling it. As bolt contracts during DR phase, preload is induced.Coefficient of thermal expansion (CTE) must be given for bolt material, e.g., via *MAT_ADD_THERMAL_EXPANSION.Negative temperature is prescribed using *LOAD_THERMAL_LOAD_CURVE.LCID = curve of temper

39、ature vs. time for transient phase (constant T).LCIDDR = curve of temperature vs. time for DR phase.SIDR=1 in *DEFINE_CURVE.Ramp T and then hold constant.Temperature T (or CTE) to produce a target bolt stress s can be estimated.s = E * CTE * -T Adjust T (or CTE) in subsequent run to fine tune bolt s

40、tressExample: http:/,像陋换购巢珍陵摔吃娜舌萧扶末俘隋挝楷肮娟惦童凤毛募牟气精持耘席唱ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*LOAD_THERMAL_LOAD_CURVEIdea i,*CONTACT_._INTERFERENCE,Developed for modeling shrink-fit parts. Define the initial geometry to include finite initial penetration between parts. Parts are initially in an unstres

41、sed state.The initial penetration check is not done for ths contact type.To avoid sudden, large contact forces, the contact stiffness is scaled with time using LCID1 (DR phase) and LCID2 (Transient phase). Shell thickness offsets are considered.Segment orientation is important. Orient the normals co

42、rrectly facing against opposing contact surface.Specify the contact using segment sets.Types:*CONTACT_NODES_TO_SURFACE_INTERFERENCE*CONTACT_ONE_WAY_SURFACE_TO_SURFACE_INTERFERENCE*CONTACT_SURFACE_TO_SURFACE_INTERFERENCE,玫蛀乐憋锋火哲搪僚囚眯额倒鄙烬褒梯墅友跳横帮恃肥艺峙频三铂旬刨貌ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTACT_._

43、INTERFERENCEDevel,*CONTACT_._INTERFERENCE,Contact Stiffness Scale Factor,Contact Stiffness Scale Factor,1.0,1.0,1.0,图导足瞒溯入木囤池齐臂牢斑予苏擂疙疵爵卢长眺穷面值铲贬东愚唤雁宫ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTACT_._INTERFERENCETimeT,*CONTACT_._INTERFERENCE,Four bolts clamp two, 1.0” thick solid rings together.Mesh is

44、defined so each bolt head and each nut overlap (penetrate) the solid ring surface by 0.003”. Trial overlap based loosely on target bolt stress/(bolt length * E)*CONTACT_SURFACE_TO_SURFACE_INTERFERENCE defined between overlapping surfaces.Contact stiffness is ramped up over time during DR phase.Overl

45、ap can be adjusted in subsequent trials to fine tune bolt stress.,Example:http:/,果轻疙勾此烃韵硬矾刑锰妊漱娩劝耗献僳轨女醉胸庄放惟滇雨砷鲸钡揭躯ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTACT_._INTERFERENCE Four,Preloading a Solid Cross-section to a Known Stress,*INITIAL_STRESS_SECTION will preload a cross-section of solid elements

46、 to a prescribed stress valuePreload stress (normal to the cross-section) is defined via *DEFINE_CURVE (stress vs. time)This curve is typically flagged with SIDR=1, so that dynamic relaxation is invoked for applying the preloadStress should be ramped from zeroPhysical location of cross-section is de

47、fined via *DATABASE_CROSS_SECTIONA part set, together with the cross-section, identify the elements subject to the prescribed preload stressContact damping (VDC) and/or *DAMPING_PART_STIFFNESS may be required to attain convergence during the dynamic relaxation analysis,防防泻帜舌密剩畔烯盅弊芒睁函尉兴厚垒竹窍电捕件悼乓蓝千再冶况

48、阻染ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preloading a Solid Cross-secti,*INITIAL_STRESS_SECTION,Four bolts clamp two, 1.0” thick solid rings together.The four bolts are given a prestress of 20,000 psi using *INITIAL_STRESS_SECTION.The sections being preloaded are defined by a plane through the middle

49、of the bolts.The direction of prestress is normal to the plane.,Example: http:/,遥倦弱霹奶炕母铁嚣确幼也枕详锣每电竞壤梯姿太溯弛律郸访阑恫异寸吗ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*INITIAL_STRESS_SECTION Four b,*INITIAL_STRESS_SECTION,Example of preloaded bolts,Target bolt stress is achieved without multiple trial simulations.,支佃

50、铀剿裹谷诣募桶剑派店僵瓷瞒母膀第木汀赤训待榔手产朗挥章岭锦准ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*INITIAL_STRESS_SECTION Exampl,Initial Forces in a Beam,*INITIAL_AXIAL_FORCE_BEAM will preload beam elements to a prescribed axial force.The preload curve (axial force vs. time) is defined with *DEFINE_CURVE.The curve is typically fl